There is a continuous growth in recent years in number of electronic apparatuses equipped with rotary type encoders for their input control units, particularly for such applications as input controllers for temperature adjustment of air conditioners mounted on automobiles.
Referring to FIG. 8 to FIG. 10, description is provided hereinafter of a conventional rotary type encoder.
FIG. 8 is a plan view showing contact positions of contact shoes and a rotary contact plate of the conventional rotary type encoder, FIG. 9 is a table showing a relation of contact positions between the contact shoes and the rotary contact plate at various positions, and FIG. 10 is a cross sectional view of the encoder taken along the line 10-10 of FIG. 8.
As shown in FIG. 10, lower case 1 made of a molded resin has an exterior with a generally annular shape, and both inner cylindrical portion 1A configuring a center hole and outer wall portion 1B protrude upward, leaving an open-top hollow portion between them. There are six electrically independent contact shoes 2 arranged in line along the radial direction on a bottom surface of the hollow portion with their points extending upward as being free ends.
Rotary body 3 is provided with flange portion 3B of an annular shape at the lower side of cylindrical portion 3A with a center hole in the center thereof. Cylindrical portion 3A of rotary body 3 is fitted in a rotatable manner on the outer surface of inner cylindrical portion 1A of lower case 1.
Flange portion 3B is provided with rotary contact plate 4 (refer to FIG. 8) on the underside thereof to generate 5 bits of absolute output. When rotary body 3 is assembled with lower case 1, six contact shoes 2 come into thrusting contact with the underside of flange portion 3B where rotary contact plate 4 is provided.
The top of the hollow portion of lower case 1 is covered with flat portion 5A of metal cover 5, which is attached to lower case 1. Metal cover 5 has center opening 5B in its flat portion 5A. Inner cylindrical portion 1A of lower case 1 and cylindrical portion 3A of rotary body 3 project upward from center opening 5B in a concentric manner, and cylindrical portion 3A serves as a control portion. A rotatable angle of operation of rotary body 3 is restricted by metal cover 5, although not shown in the figures.
Rotary contact plate 4 has a configuration, which is described now by referring to FIG. 8. Rotary contact plate 4 comprises a common conductive portion of an annular shape exposed in the innermost area, and a signal conductive portions exposed in a peripheral area surrounding the common conductive portion. These exposed conductive portions are hatched in FIG. 8 to make them easily discernible. In addition, black dots are added to indicate points where contact shoes 2 are in contact with either the underside of flange portion 3B or rotary contact plate 4 on rotary body 3.
These conductive portions are electrically continuous throughout, and they are so configured that they produce 32 variations of detectable output modes, as shown in FIG. 9, when six contact shoes 2 come into contact therewith at each of thirty-two (32) angular positions within a range of the rotatable angle, which is divided into thirty-one (31) parts at equal angular intervals. Circular marks in FIG. 9 indicate positions where contact shoes 2 come into contact with, and therefore have electrical continuity with rotary contact plate 4.
FIG. 8 shows one of the positions in the range of the rotatable angle, and that rotary body 3 is rotatable from this position to an angle of 279° as shown by an arrow indicating the clockwise direction in this figure.
In the conventional rotary type encoder constructed as described above, cylindrical portion 3A is turned to rotate rotary body 3 and move positions where six contact shoes 2 (i.e., COM and SIG1 to SIG5) come into contact with rotary contact plate 4 on the underside thereof, thereby making it capable of detecting an output mode corresponding to the angular position.
Detection of the output mode is achieved by checking presence or absence of continuity of each of five contact shoes 2 (SIG1 to SIG5) with respect to common contact shoe 2 (COM) provided at the innermost position through the signal conductive portions conductively linked with the common conductive portion.
There are a number of prior art documents known to be related to the invention of this application, including Japanese Patent Unexamined Publications, Nos. 1989-152314 and 2005-172552, for example.
There is a problem, however, with the conventional rotary type encoder described above in that it has a large external size due its structure having the six contact shoes 2 mounted along the radial direction.